A communication scheme called OFDMA (Orthogonal Frequency Division Multiple Access) where transmissions to a plurality of wireless communication terminals (hereinafter referred to as terminals) or receptions from a plurality of terminals are simultaneously performed is known. Particularly, OFDMA where one or a plurality of subcarriers is assigned to a terminal as a resource block and the transmissions to the plurality of terminals or the receptions from the plurality of terminals are simultaneously performed on the resource block basis is also called resource-block-based OFDMA. The simultaneous transmissions from a base station to the plurality of terminals correspond to downlink OFDMA transmission and the simultaneous transmissions from the plurality of terminals to the base station correspond to uplink-OFDMA transmission.
A communication scheme called uplink multiuser MIMO (Multiple-Input Multiple-Output) is known where streams are transmitted from the plurality of terminals to the base station by spatial multiplexing (simultaneously by the same frequency band), and the base station simultaneously receives these streams by a plurality of antennas. Moreover, a scheme called downlink multiuser MIMO where the streams are transmitted from the base station to the plurality of terminals by spatial multiplexing (simultaneously by the same frequency band) and each terminal receiving each stream transmitted to itself is also known.
When uplink OFDMA (UL-OFDMA) or the uplink multiuser MIMO (UL-MU-MIMO: Uplink Multi-User MU-MIMO) communication is to be performed, it may be considered that a base station transmits a trigger frame in order to align the uplink transmission timings of each terminal. By each of the terminals performing transmission after certain time from the reception of the trigger frame, the transmission timings are aligned whereby the uplink multiple transmission (UL-OFDM or UL-MU-MIMO) is realized. Before the transmission of the trigger frame, scheduling including determination of matters required for uplink multiple transmission such as selection of terminals to be targets of the UL-OFDMA or UL-MU-MIMO or parameter information of the transmission is needed, but since the resource of the communication is limited, the scheduling which can improve system efficiency as much as possible is in demand. If a terminal not having data to be transmitted is selected as a target terminal, for example, the communication resources assigned to the terminal are not effectively used in an uplink transmission period, and it is likely that the system efficiency degrades. Moreover, if a base station tries to collect information from each terminal in advance in order to efficiently determine the required matters, processing at the base station becomes complicated, and if a collection period gets longer, it is likely that the system efficiency degrades.